This invention relates to a powerline carrier control installation in general and more particularly to a simplified installation of this type.
Powerline carrier control installations including a powerline carrier control transmitter which supplies an audio frequency output voltage; an isolation transformer fed on the primary side by the audio frequency output voltage and connected on the secondary side via a coupling capacitor in parallel to an a-c voltage network of given line a-c voltage and line frequency, the line frequency being somewhat lower that the audio frequency of the output voltage; a resonant circuit formed by the coupling capacitor and an inductance and whose resonant frequency is at least approximately tuned to the audio frequency; and a device arranged on the transmitter side of isolation transformer for suppressing a line-frequency feedback transmitted from the network side are known.
In a powerline carrier control installation with parallel coupling to the a-c voltage network, the audio frequency output voltage generated by the powerline carrier control transmitter must be brought, in a suitable manner, to the feed plane, that is, to the a-c voltage network, which may, for example, be a distribution system feeder a-c voltage network e.g., at about 10 Kv. The coupling unit required for this purpose should, for reasons of cost as well as of space, transport the audio frequency power generated by the powerline carrier control transmitter to the feed plane without any great losses and using as few parts as possible. At the same time, the coupling unit must intercept a-c voltage. In addition, the device for suppressing a line frequency feedback must make sure that the line frequency and its harmonics are kept away from the powerline carrier control transmitter to the extent that the latter is not disturbed in its operation.
A powerline carrier control (PCC) installation of the above mentioned kind with parallel coupling is illustrated in a single-phase, for example, in FIG. 1 of West German Patent Application DE-OS No. 2 461 564. Here a PCC installation where the parallel coupling us designed as a so-called "suction circuit coupling" is involved. The PCC transmitter feeds its audio frequency output a-c voltage to the primary winding of an isolation transformer. The secondary winding of the isolation transformer has its one end connected, via a series connection consisting of a coupling capacitor and a coupling choke, and its other end connected directly to a single phase a-c voltage network. The transformation ratio of the isolating transformer is normally, in existing installations, in the range of about 0.5:1 to 2:1, more particularly 1:1. The coupling capacitor and coupling choke are rated so that together they form a resonant circuit for the audio frequency. This resonant circuit acts as a suction circuit for the audio frequency output a-c voltage of the PCC transmitter. The suction circuit is damped essentially only by the ohmic portion of the load, that is, of the a-c voltage network. The coupling choke may be designed as a tuning choke to permit compensation of manufacturing tolerances of the suction circuit components and adaption to the reaction component of the network impedance. The loss resistances of the coupling elements (coupling choke and coupling capacitor) as well as the magnetization and leakage inductances of the isolation transformer may be negelcted in an evaluation of the mode of operation of such a powerline carrier control installation. In the known powerline carrier control installation, an audio frequency current supplied by the PCC transmitter, transmitted through the isolation transformer and flowing successively through the coupling choke and the coupling capacitor is coupled into the a-c voltage network. A line-frequency current (backward current) flows through the resonant circuit and is transmitted from the isolation transformer to the transmitting side again. Since this backward current has a disturbing effect on the PCC transmitter, a device for suppressing a corresponding line frequency feedback is provided on the transmitter side of the isolating transformer. What is involved here is a so-called resonance shunt, which takes over the backward current. In the known PCC installation, this resonance shunt consists of a suction circuit rated for line frequency, namely the series connection of a capacitor with a choke, this series connection being connected in parallel with the primary winding of the isolating transformer. In parallel with this series connection is a further capacitor, to compensate the effect of the suction circuit on the audio frequency output a-c voltage of the PCC transmitter. In a three phase form of construction the suction circuit coupling device consists of a three phase coupling capacitor battery, three coupling chokes in the form of tuning chokes, a three phase isolating transformer, and a three phase resonance shunt.
A characteristic feature of the known parallel coupling arrangement is that the PCC transmitter acts as a current source for the audio frequency current and is connected in series with the coupling elements (coupling capacitor, coupling choke) and with the network load. Thus the same current flows through PCC transmitter, the coupling elements and the network load.
It has been found that in a PCC installation with parallel coupling, the coupling unit is expensive and requires a considerable amount of space.